Typically, in a ring-type network (hereinafter, referred to as “ring network”), transmission apparatuses constituting the ring network communicate packets with one another. Each of such transmission apparatuses sits on top of a separate local network. From a device constituting the local network established under a particular transmission apparatus, a packet is transmitted to a device constituting the local network established under another particular transmission apparatus via other transmission apparatuses constituting the ring network.
Once a transmission apparatus receives a packet, it stores that packet in a buffer memory or the like on a temporary basis and then transmits the packet to a device specified as the destination address in the corresponding local network. Herein, in that state of the buffer memory in which no more memory capacity is available (hereinafter, referred to as “memory full state”); the transmission apparatus cannot transmit the packet to the corresponding local network. Hence, the transmission apparatus destroys that packet. As a substitute for the destroyed packet, the source apparatus resends a packet.
Meanwhile, regarding the issue of the memory full state, a technology is known in which a backup memory area is secured and the transmission apparatus is maintained in the duplexed state. Moreover, regarding the issue of the memory full state, another technology is known in which the packets are first sent to a device constituting the local network of another transmission apparatus having free buffer memory and then sent to a device specified as the destination address via a different transmission path. Another technology is known in which the inward traffic of packets is restricted in the source transmission apparatus.
However, in the conventional technologies, the packets transmitted in the ring network suffer from degradation of transmission efficiency and reliability. More particularly, in the technology of securing a backup memory area and maintained the transmission apparatus in the duplexed state, an increase in the number of devices or apparatuses may lead to an increase in the rate of occurrence of failures. Eventually, that results in the degradation of quality and reliability. In the technology of transmitting a packet via a different transmission path, the header of the packet frame undergoes transformation and the memory is burdened in the other device receiving the packet. That results in the degradation of reliability. In the technology of restricting the inward traffic of packets, the transmission quantity as well as the transmission efficiency undergoes degradation.
Patent Document 1: Japanese Laid-open Patent Publication No. 2008-153884
Patent Document 2: Japanese Laid-open Patent Publication No. 2006-033348
Patent Document 3: Japanese Laid-open Patent Publication No. 06-276207